In general, the invention relates to a detection apparatus that is able to detect hydrogen (for instance for detecting an amount of water) in an object by use of a neutron source. A neutron source for this purpose presents the advantage in that neutrons are able to penetrate certain barriers. For instance, it is possible by this invention to estimate the amount of hydrogen, water and/or humidity in, for example, insulation material arranged in a steel pipe. It can be used for checking whether and how much water/humidity there is present in the insulation material, which is important to know, for example, in connection with the assessment of the risk of corrosion, rust, etc. This may be performed without having to remove or cut in parts of the pipe/object or to separate the object/pipe or parts thereof.
A source of fast neutrons emits fast/energy-rich neutrons, therefore neutrons with high kinetic energy. In the present invention the known discovery is used to advantage that atomic nuclei (and in particular hydrogen) brake neutrons upon collision, a phenomenon typically referred to as elastic scattering/collision (whereby the velocity is reduced and the direction is changed for a collided neutron). This invention uses a detector device that detects relatively slow/energy-poor neutrons, the so-called thermal neutrons. After a neutron has been braked sufficiently, it can be detected by the detector device. The process of braking neutrons is typically designated ‘moderation’ and a physical arranged for this a ‘moderator’. In order for a neutron to be detected, most often is has to collide several times with hydrogen atoms.
In order to accomplished an increased sensitivity it is known to configure the detection apparatus to comprise an (auxiliary) moderator, an amount of hydrogen or a moderator material that brakes and reflects/scatters neutrons by elastic scattering/collision and is arranged such that a portion of incoming neutrons are reflected against the detector and the hydrogen for detection. In broad outline the further amount of hydrogen/moderator material serves as a (partial) neutron reflector that also brakes the neutrons, thereby causing a larger amount of braked/thermal neutrons to be detected. This is also often referred to as neutron back-scatter.
Patent specification GB A 1180450 discloses an arrangement for detecting humidity/hydrogen by use of a neutron source. The arrangement according to GB A 1180450 is shown schematically in FIG. 1 and comprises a fast-neutron source (103), a detector for thermal neutrons (102) and a hydrogen-containing neutron-braking and -reflecting/-scattering material (therefore moderator material) (104) for providing the back-scatter effect, wherein the detector (102) and the source (103) are arranged between this material (104) and the material/object (101) in which the humidity/water/hydrogen is to be detected.
It is mentioned in patent specification GB A 1180450 that the detector of thermal neutrons (102) may be a scintillator.
Albeit the detector according to GB A 1180450 has an increased sensitivity due to the moderator (104), it is possible to accomplish superior sensitivity as taught by the present invention.
Patent specification U.S. Pat. No. 3,707,631 relates to a system for non-destructive analysis of nuclear fuel, wherein a neutron source and a detector device are arranged to each their side of the sample. The source emits low-energy neutrons (<1 Mev), therefore not thermal, where a comparatively large moderator brakes the emitted neutrons to the effect that they can initiate a fission process that emits fast (>1 Mev) neutrons that are detected in an energy-selective scintillator. In this system, measurement is performed on fast neutrons and various measures must be taken to separate them from the (almost equally) fast neutrons from the source that have not been braked. A light guide is also mentioned, the primary function of which is to couple a number of very different scintillator geometries to the front of a standard photo-multiplier.
The arrangement disclosed in U.S. Pat. No. 3,707,631 is not directed against or suitable for the detection of hydrogen.
Patent specification No. U.S. Pat. No. 5,446,288 teaches detection of hydrogen and other light elemental substances using detection of when thermal neutrons, where light source and detector are on the same side of the sample. A detector device comprises a scintillator coupled to a photo-multiplier via a light guide in the form of an air light guide, wherein the neutron source is enclosed by moderator material that is separated from the light guide.